1. Field of the Invention
The present invention relates to a connection structure for a light transfer medium which is embedded in a structural body of the connection structure and used for communication or a sensor, and a method of manufacturing the same.
2. Description of the Related Art
A structural body of a connection structure for a light transfer medium is structured so as to embed optical fiber which is a light transfer medium to transfer an optical signal. Further, the optical fiber embedded in the structural body makes it possible to detect changes of the optical signal transferred in the optical fiber such as changes in the light intensity and wave length. Thus, internal damage or distortion of the structural body can be detected.
The structural body is formed by overlaying and hardening prepreg (an abbreviation for pre-impregnated materials) sheets in the direction of the plate thickness. Each prepreg sheet is an intermediate base material to be formed, which is produced by pre-impregnating a reinforced fiber base material with matrix resin.
The structural body is formed in such a way that a plurality of prepreg sheets are laminated and formed as a precursor, and the precursor is bagged, decompressed, and deaerated and then formed and processed by heating and pressurizing by an autoclave. Thus, an intermediate product is formed and partially cut off, and the residual part is formed as a structural body. In the process of forming a structural body like this, optical fiber is embedded in the structural body.
The optical fiber embedded in the structural body is extended outwardly from the inside of the structural body beyond the end face of the structural body. The outwardly extended optical fiber, after forming of the structural body, is connected to optical related devices such as a light source and a light measuring instrument. As a conventional art for outwardly extending the optical fiber from the inside of the structural body, there is a method of outwardly extending the embedded optical fiber directly from the end of the structural body available.
FIG. 14 is a sectional view showing the state of decompression and deaeration of a bagged precursor 21 before heating and pressurization. A manufacturing method of a structure for outwardly extending optical fiber directly from a structural body will be explained with referring to FIG. 14. The precursor 21 is covered with a bagged film 23 composed of a nylon film and a storage space 26 for storing the precursor 21 is airtightly sealed by a vacuum bagging seal material 24. The storage space 26 is evacuated by a vacuum pump not shown in the drawing and deaerated through a evacuation hose 27.
As the space 26 storing the precursor 21 is deaerated, a pressurizing sheet 28 composed of an aluminum sheet or an FRP (fiber reinforced plastics) sheet presses the surface of the precursor 21, and the precursor 21 is put into an autoclave in such a state, and the storage space 26 is heated and pressurized, and the precursor 21 is formed by a jig 29, the pressuring sheet 28, and a dam 25.
When optical fiber 22 is extended directly from the side of the precursor 21, the optical fiber 22 may be damaged during evacuation in the neighborhood of the side of the precursor 21. Further, when the length of the optical fiber 22 outwardly extended from the precursor 21 is short, during heating and pressurizing, there is the possibility that resin may flow out from the precursor 21 and the resin may reach one end of the optical fiber 22.
To solve such a problem, an art for covering the part of the optical fiber outwardly extended from the precursor 21 with a pipe is conventionally considered. This conventional art will be explained by referring to FIGS. 15 and 16.
FIG. 15 is a perspective view showing the structure of another conventional art in which optical fiber 3 is outwardly extended from the end face thereof. In a structural body 1, a tube 4 having a circular cross section made of Teflon (R) having a projection 4a projected out of one side 2 is installed. The optical fiber 3 embedded in the structural body 1 passes through the tube 4 and extends outwardly from the structural body 1. By doing this, the optical fiber 3, during evacuation, can be prevented from damage to the outwardly extended part thereof. Further, there is a case that an embedding type connector is embedded in place of the tube 4.
FIG. 16 is a perspective view showing the structure of another conventional art in which optical fiber 6 is outwardly extended from the end face thereof. In a structural body 5, a tube 7 of a circular cross section having a projection 7a projected out of one surface 8 in the direction of the sheet thickness is installed. The optical fiber 6 embedded in the structural body 5 passes through the tube 7 and extends outwardly from the structural body 5. By doing this, in the same way as with the conventional art shown in FIG. 15, the optical fiber 6, during evacuation, is prevented from damage to the outwardly extended part of the optical fiber 6.
For an intermediate product in the state after heating and pressurizing of the precursor, a trimming process of cutting off an unnecessary periphery is performed. The intermediate product subjected to the trimming process is formed as a structural body and the structural body is formed in a predetermined size. In the conventional structure in which the optical fiber 3 is outwardly extended shown in FIG. 15, due to the projection 4a of the tube 4 projected from the one side 2 of the structural body 1, the trimming process cannot be performed for the intermediate product in the state before forming the structural body and a problem arises that it is difficult to form the structural body in the predetermined size.
Further, when an embedding type connector is to be embedded in place of the tube 4, since the volume of the embedding type connector is larger than that of the tube 4, an another problem arises that the thickness of the structural body at the part of the structural body where the embedding type connector is embedded becomes smaller. Thus, a remarkable reduction in the strength of the structural body 1 is caused. When the problem of the strength reduction is solved by thickening the thickness of the structural body at the part where the connector is embedded, another problem arises that the connector embedding part of the structural body requires padding up, that is, an excess thickness.
Further, in the structure in which the optical fiber 6 is outwardly extended shown in FIG. 16, the projection 7a projected in the direction of the sheet thickness of the structural body 5 is formed, as aforementioned. In such a structure, in the state of decompression and deaeration of the precursor, since the projection 7a is projected on the surface 8 in the direction of the sheet thickness, a problem arises that it is difficult to press the side of the precursor in the direction of the sheet thickness which is the surface to be pressed by the pressurizing sheet 28 shown in FIG. 14 so as to make it flat.
Further, when in the state that the optical fiber 3 is outwardly extended directly from the side of the intermediate product, the optical fiber 3 is to be trimmed and cut, the end face of the optical fiber 3 is damaged by the trimming process. Therefore, after the trimming process, the end face of the optical fiber 3 must be ground. As mentioned above, since a step of grinding the end face of the optical fiber 3 is required after the intermediate product is trimmed, a problem arises that the manufacturing process is complicated and the optical fiber 3 cannot be easily connected to another optical fiber.
Further, as shown in FIG. 14, in the state of decompression and deaeration of the precursor, in order to prevent one end of the optical fiber 22 from being covered with resin, when the one end of the optical fiber 22 is extended out from the bagged film 23 using the tube 4 or 7 shown in FIG. 15 or 16, a gap is inevitably formed between the tube 4 or 7 for protecting the optical fiber 22 and the vacuum bagging seal material 24 shown in FIG. 14, and poor deaeration is caused, and defective formation of the precursor is caused.
Further, as mentioned above, when the optical fiber is to be extended out from the structural body, in order to ensure the length necessary to connect to the light measuring instrument, the optical fiber 22 is lengthened. When the optical fiber 22 is lengthened, the handling thereof becomes difficult and as compared with a case of no-existence of the optical fiber 22, the operability of manufacturing of the structural body is reduced.